This invention relates to control systems and more particularly to adaptive control systems for use in tuning a plant in which the control parameters are determined and effected automatically based upon a desired system performance.
Briefly, by way of background, a plant is the controlled element in a system. It is a body, process, or machine, of which a particular quantity or condition is to be controlled. A controller is employed to control the particular quantity or condition of the plant. An adaptive controller performs this type of control in real-time. That is an adaptive controller performs real-time data manipulation to determine and implement control parameters used to produce a satisfactory and consistent response by the plant.
Long range application systems employ controllers for precise tuning of the line-of-sight and line-of-sight rate for use in directing, pointing, tracking and rate control applications for laser, inertial navigation, photography, and radar systems. For example, long range photographic camera systems are employed to provide high resolution reconnaissance photographs from large stand-off distances thereby greatly enhancing mission safety and survivability. Imaging from exceedingly long distances requires a precise image stabilization system to minimize distortions caused by aircraft motion. Further, the long range photographic camera systems' directing, pointing, tracking and rate units require precise tuning to remove or suppress any undesirable characteristics of the components used in the systems and thereby tune the system.
In the environment of long range photographic equipment systems, the plant generally includes a power amplifier, a motor, a gimbal, a mirror and a gyroscope. The power amplifier and motor are employed to precisely control the line of sight, for example, of the laser or camera. One or more inertial rate-integrating gyroscopes mounted on the laser or camera platform serve as angular motion sensors. A feedback device may be employed to measure acceleration, velocity and/or position of the platform.
The control loop or controller generally includes filters and compensators to perform system tuning to remove or reduce any non-idealitics of the components, for example, resonances due to the gyroscope and/or motor. Conventional long range application systems employ analog filters and compensators in the control loop of the rate unit. The filters and compensators are designed from discrete analog components, for example, discrete inductors, capacitors and/or operational amplifiers. They often include potentiometers that facilitate precise filter tuning as well as subsequent "tweaking" when necessary.
Systems employing an analog tuning require an experienced and skilled technician to tune the analog circuits to thereby provide a desired system response. This generally requires utilizing a spectrum analyzing device to measure and characterize the frequency response of the system. Each filter and compensator is then tuned so that the system attains the desired performance specifications.
Analog tuning systems often require many adjustable components to implement a precise tuning network. This often leads to a time consuming and complex tuning procedure that must be performed for each tuning network of each module. Further, analog tuning systems are often complex designs that tend to be very large and bulky in environments under great space constraints.
Employing an adaptive control system alleviates the need for analog filters and compensators used in tuning the system. One such conventional adaptive control system employs a pole-placement method to determine the parameters of the compensator. For example, Goodnick and Lau in "Adaptive Control Algorithm Self-Tunes Industrial Servo," Intelligent Motion, September 1989, pages 26-32, describe an adaptive control system employing a pole-placement method to determine a compensator's control parameters for self-tuning to a specified closed loop response. Briefly, in a pole-placement compensator design control algorithm, the system designer specifies the system's closed loop dynamics. Input and output data determine open loop process parameters. The system uses these parameters to compute the
compensator coefficients or parameters.